If you’re rowdy, you’re loud and raucous. You’re disturbing the peace and somebody’s likely to ask you to quiet down.
When your team wins, if you and your teammates celebrate by running through the streets screaming and wrestling each other on people’s lawns, you’re a rowdy bunch. You may be rough and obnoxious or just rowdy in a good-natured way. But you reserve the name rowdy for a cruel and brutal guy. Remember that bully in the seventh grade who kept taking your lunch money? He was a rowdy.